The present invention relates to a technique for detection of trace amounts (at a ppb to ppt level in concentration) of water-soluble chemically contaminating impurity constituents contained in air inside a clean room. The invention is suitably applied to a method of detecting chemically contaminating impurity constituents in a gaseous or molecular state, evolved from constituent members of a building used as a clean room of a semiconductor manufacturing plant, or manufacturing equipment installed inside the clean room, chemicals used in a manufacturing process, constituent components of auxiliary facilities such as service supply facilities, humans themselves, and so forth, including, for example, chemically contaminating impurity constituents of acidic, basic, condensate (organic substance) series, and dopant series, and constituents of compounds thereof.
As for control of contamination on the surface of semiconductor silicon wafers, it has become important to control surface contamination (cleanliness), surface shape, and residual surface distortion (crystallinity). In a manufacturing process at a semiconductor manufacturing plant and a liquid crystal manufacturing plant, besides adverse effects of fine particle contamination and metallic contamination, chemical contamination such as adsorption contamination, chemical reaction contamination, or condensation contamination of chemically contaminating impurity constituents on the surface of silicon wafers and lenses for the manufacturing equipment such as photolitho stepper, acting as factors of deterioration in reliability and yield, has given adverse effects on the surface of products (silicon wafers) processed in a manufacturing process line, thereby causing problems of various quality deteriorations. Examples of factors causing such quality deteriorations include various chemically contaminating substances in gaseous or molecular state, present in air inside the clean room, and evolved from sources of evolution such as the constituent components of the building, the manufacturing equipment, the chemicals used in the manufacturing process, the constituent components of the auxiliary facilities, humans, etc. and compounds thereof.
More specifically, in the air inside the clean room, there exist not only fine particles but also four species of constituents as chemically contaminating impurity constituents present in mixed state, which can be classified as follows, although this is dependent on variation in process conditions of a manufacturing process line:    1. acidic series substances: corrosive substances having a chemical reaction behavior such as one so as to accept electrons (hydrofluoric acid HF, sulfur oxides SOx, nitrogen oxides NOx, etc.)    2. basic series substances: corrosive substances having a chemical reaction behavior such as one so as to donate electrons (ammonia NH3, amine, etc.)    3. organic series substances: chemical substances having a boiling point higher than room temperature under normal pressure, and undergoing condensation on a clean surface (siloxane, phthalate, HMDS, BHT, etc.)    4. dopant series substances: chemical elements having tendency of causing a change in the electrical characteristic of semiconductor devices such as a transistor and capacitor (boron B, phosphorus P, etc.)
These chemically contaminating impurity constituents in gaseous or molecular state undergo chemical reaction with each other or condensation growth due to a change in environmental conditions inside the clean room, and are transformed into fine particles or compounds in gaseous or molecular state, having different properties, to be thereby adhered to the surface of wafers during a manufacturing process as surface contaminating constituents, thus creating a cause for unstableness in process conditions or a cause for deterioration in yield.
In normal operating conditions, there always occurs evolution of these chemically contaminating impurity constituents in a constant amount and in a constant concentration in a steady state of circulating air of an air conditioning unit of a circulating system flowing along the flowing direction, and the chemically contaminating impurity constituents are carried directly to wafers, a container for transporting the wafers, and the surface of lenses disposed in a manufacturing equipment, which are exposed to an air flow path, to be thereby adhered or adsorbed thereto due to physical or chemical reactions. Further, in operating conditions of manufacturing equipment in an unsteady state as well, there occurs evolution of chemically contaminating impurity constituents in a considerably larger amount than in a normal case, and the chemically contaminating impurity constituents are carried to wafers, a container for transporting the wafers, the surface of glass, and the surface of lenses inside a stepper equipment, which are exposed to the air in the cleaning room, to be adhered or adsorbed thereto due to physical and chemical reactions.
As a method of detecting impurities in the form of fine particles floating in air among the chemically contaminating impurity constituents, there has been known a physically counting method by a laser scattering technique, using a particle counter. Further, as a method of measuring water-soluble chemically contaminating impurity constituents affecting wafer quality due to primary chemical reactions, there has been known a method employing the impinger method for dissolving impurity constituents in pure water, and the ion chromatography for subsequently identifying the impurity constituents. Still further, as a method of detecting chemically contaminating impurity constituents of acidic, basic, condensate (organic substance), and dopant series, respectively, there has been known a detection method combining the solid abstraction method for physically adsorbing these impurity constituents to adsorbents with the gas chromatography.
As for a method of detecting impurity constituents contaminating the surface of wafers, there has been known the liquid abstraction method for dissolving the impurity constituents in a chemical liquid (for example, hydrofluoric acid, and so forth) as a method of measuring water-soluble chemically contaminating impurity constituents affecting wafer quality due to secondary chemical reactions. Further, as a method of detecting organic substances, there have been known a detection method combining the solid abstraction method for physically adsorbing these impurity constituents to adsorbents with the TOC analytical method, and the SIMS method. Still further, as a method of detecting impurity constituents of inorganic metal ions, there have been known the vapor-phase cracking method and the total reflection fluorescent X ray analysis method. Yet further, as a analytical method of detecting adsorbing molecules, there have been known the thermal desorption spectroscopy (TDS) and the Time of Flight Mass Spectroscopy (TOF-SIMS) analytical method. Any of the detection methods described above has the following feature.
Firstly, in the case of detecting fine particles, fine particles down to 0.05 μm in grain size can be counted by the laser scattering method, however, an interrelation between a shape of the fine particles and a counting device is important. As a method of finding out the concentration of ultrafine particles, in number, there is available a condensation nucleus counter. This is a method wherein an atmosphere around ultrafine particles is turned into supersaturation state by any method using alcohol, water vapor, and so forth, causing vapor around the ultrafine particles to undergo condensation growth to thereby optically detect the number of the ultrafine particles.
In the case of detecting organic substances, a method of absorbing organic carbons is important in the absorbing method. With the SIMS analytical method, analysis of bacteria, and so forth, and determination of contaminated spots are important.
In the case of detecting inorganic metal ion impurities, evaluation of concentration, down to a level of 109 atoms/cm2, and nondestructive evaluation of distribution within a wafer surface are feasible, however, dependency on recovered liquid species, and high sensitivity are important.
Further, in the case of detecting adsorbing molecules, evaluation of an adsorption state, and quantification of water molecules, contaminating constituents, and so forth, are important in the TDS analytical method. With the TOF-SIMS analytical method, analysis of light elements is feasible, however, high sensitivity and quantification are important.
However, there is the following problem with any of the detection methods described above, such as the laser scattering method, chemical reaction adsorption-separation method, electron beam or X-ray irradiation method, and thermal programmed desorption analytical method.
Firstly, in the case of detecting fine particles by the laser scattering method, fine particles less than 0.05 μm in grain size can not be counted, and it is necessary to check the interrelation between the shape of the fine particles and the counting device. There occurs a problem in that sufficient scattering signals can not be obtained in terms of an S/N ratio when a grain size is not more than 0.1 μm.
Further, in the case of extracting the organic substances by the adsorption-separation method, the method of extracting the organic carbons is difficult to perform, and there is a problem with the Secondary Ion Mass Spectroscopy (SIMS) analytical method in that analysis of bacteria, and so forth, and determination of the contaminated spots are not possible to implement.
In the case of detecting metal ion impurities by use of electron beam or X-ray, evaluation of concentration at a level less than 109 atoms/cm2 is unfeasible, and there is a problem with dependency on the recovered liquid species, and high sensitivity. This method has a problem in that it is dependent on the shape and species of fine particles, and microscopic asperities on a wafer surface are detected as measured values.
Further, in the case of detecting the adsorbing molecules by the TDS analytical method, quantification and identification is difficult to achieve due to a change in adsorption and release states of water molecules, and so forth, and a change in surface property and crystalline condition of adsorption surfaces. For example, it is not possible to perform analysis of heavy elements by the TOF-SIMS analytical method, which has a problem with high sensitivity and quantification.
That is, with any of the detection methods described in the foregoing, there is a problem in that detection is effected by reaction, decomposition, or dissociation, taking place only once, and consequently, it is not possible to separate interfering constituents simultaneously interfering with each other.